A dialect of typing that uses numbers and symbols to replace letters, and many misspellings. The name is a bastardization of "elite speak", as it was originally popularized to "look cool" and seperate one from word=noobnoobs/word.
Examples of such replacements used in leetspeak are: 1's or |'s for l's and/or i's, 5's or z's for s's, @'s or 4's for a's, \/\/'s for w's, etc. People who use l33tspeak usually have their own form, using their own combinations of replacements and misspellings.
A popular form of l33tsp33k uses random capitalizations of letters that are not (or cannot be, in some cases) replaced.
Nowadays computer geeks, and those who spend much of their day in word=chat roomchat rooms/word or word=forumforums/word will use intermittent l33tsp33k to joke around with one another; true l33tsp33kers are rarely seen around the internet anymore.

leet or elite speak, an almost dead internet language originally used by real hackers to communicate, now used by people trying to make themselves look cool by typing in a language hardly anyone can read, here is a quick tutorial on how to speak 1337.

l33tspeek is a term that came about with the early hacker, sometimes called elite speak. Someone who spells in l33tsp33k with pride is someone who can type it as fast as normal words. There are many other spellings, such as the number based 13375P33|< or the rarely seen |337zp33|{.

7|-|15 |5 3><7R3/\/\3 |3375P33|{

Translation: This is extreme l33tsp33k
Notice that there are only two actual characters used, r and p.

in simple terms, a "language" for morons. generally members of an online gaming community will type like this, leading them to believe that they are funny and/or cool. the causes of them wanting to look like morons are unknown. see also: teh and pwned

online gamer: d00d!!!1 joo jus got mega pwnz0rd!! LOL @ joo n00b!

normal person: you sound like a dipshit. learn to speak english, isn't that something we were all taught in first grade?

1.no one understands what the fuck you are saying
2.it is not funny (but people will laugh... haha)
3.its a waste of your worthless time
4.you look like a fucking idiot
5.you are not cool, and typing like that does not improve your status whatsoever
6.it proves that you have not completed your quest for punani and will not succeed for a long time